In the manufacture of an automobile, one of the more expensive components is of course the automobile engine, and a relatively expensive component of the automobile engine is the cast cylinder head. Hence, an industry has existed for many years to rebuild major components of an automobile engine so that an automobile owner in need of a new engine or a new cylinder head can save substantial amount of money by purchasing a rebuilt engine or rebuilt cylinder head rather than new factory parts.
In recent years, aluminum cast engine parts, especially aluminum cast water cooled cylinder heads have become more popular, primarily because of their light weight characteristic. For example, aluminum cylinder heads are now used on the best selling car in the world, the Ford Escort. However, aluminum also has certain disadvantages. For example it lacks the hardness of iron and hence it is more expensive to machine. Aluminum expands and contracts at approximately twice the rate of cast iron in response to temperature changes, thus creating the possibility for thermal induced stress, especially since this aluminum head is generally mounted on a cast iron block which expands and contracts at half the rate of aluminum. Increased thermal expansion and contraction in turn increases the possibility of stress related cracks. The most probable areas for cracks include the areas around the valve seats or between the intake and exhaust seats or just under the exhaust seats. The industry of renewing cylinder heads has existed for decades, and because of the tremendous importance of aluminum cylinder heads, as discussed above, the industry has already been developed to renew them, i.e., rebuild them in an attempt to arrive at a completely renewed cylinder head of sufficient quality to be assembled onto an engine block for use in an automobile.
However, until now the various attempts at renewing aluminum water cooled cylinder heads have been relatively unsuccessful. The yield of rebuilt cylinder heads which actually performed successfully in subsequent use is thought to be as low as 50%. Considering the large and growing importance of aluminum cylinder heads, a critical need now exists for updating current technology to increase the quality and hence the yield of renewed aluminum cylinder heads.
The state of the art prior to the filing of the present application is best described in a number of trade journal magazine articles including the following:
"Saving Aluminum Heads" by Larry Carley, Automotive Rebuilder, September 1986; PA0 "Flat Out" by John Decker, Motor, April 1987; PA0 "Straight Heads--Magic Is Not Needed" by Gary Lewis and Dimetri Elgin, Automotive Rebuilder, November 1985; PA0 "Welding Techniques, Part II" by Jerry Heasley, Motor, October 1984; PA0 "Welding Aluminum Cylinder Heads, How To Do The Impossible" by Vern Heinrich and Mike Pankartz, Renews, March 1987; and PA0 "Escort Heads--Making Repairs" by Jim Hughes, Automotive Rebuilder, December 1987.
In addition, rebuilding of an aluminum cylinder head is described in U.S. Pat. No. 3,192,618, issued July 5, 1965, although this patent relates to the rebuilding of an air cooled aircraft cylinder head, the renewal process for which would be substantially different than for a water cooled automotive type aluminum cylinder head.
Thus, a need exists for new and improved processes for renewing aluminum cylinder heads, especially water cooled aluminum cylinder heads of the automotive type, which processes will overcome the major disadvantage of prior techniques by providing a substantially higher yield of acceptable, operable cylinder heads and, correspondingly a substantially lower percentage of failures.